1. Field of the Invention
The present invention pertains to fluid delivery systems, and more particularly, to a simplified fluid delivery system that substantially prevents the measurement of a multiphase fluid flow during the delivery of a fluid product from a source to a destination.
2. Statement of the Problem
Fluid delivery systems are designed to deliver various types of fluid products from a source to a destination. Some examples of these products include petroleum products, such as liquid petroleum gas, gasoline, kerosene, oil and other similar products. Other examples of these products, include agricultural chemicals, corn syrups, milk and corn sugars. The source is often a truck, railroad car, or sea going vessel, with the destination being a storage vessel located at a processing plant or dock. Similarly, the opposite is also true where the source is the storage vessel and the destination is a truck, railroad car, or sea going vessel.
Fluid delivery systems typically include, a pump connected to the source, which provides the required pressure to move the fluid through the system from the source to the destination. A strainer connected to the pump is used in some, but not all applications, to provide filtration from the intrusion of grit and other foreign matter that can damage downstream components such as the meter. The meter is typically a positive displacement or turbine volumetric measuring device that measures a volume of the fluid as the fluid is delivered from the source to the destination.
It is a problem in fluid delivery systems to prevent the measurement of entrained air or vapor in the fluid during delivery. For example, as the source of the fluid is emptied, pressure from the pump can break the surface tension of the remaining fluid in the source causing a multiphase flow of air and fluid to be pumped through the delivery system. When this occurs, the volumetric meter cannot differentiate between a pure fluid flow and the multiphase fluid flow comprising both the air and fluid.
One solution to this problem is to use an air eliminator to separate and remove undesired air or vapor from the fluid prior to delivery to the meter. An air eliminator removes entrained air by decreasing the velocity of the fluid to a relatively calm state by permitting the fluid to accumulate in a chamber in the air eliminator. The substantial decrease in velocity causes trapped air bubbles or vapor to rise out of the fluid and collect in the upper portion of the chamber where it is vented. The air eliminator also prevents damage to the meter by preventing large amounts of air from passing through the meter. Large amounts of air passing through the meter can cause over-speeding of the measuring unit or excessive wear that eventually results in meter failure.
Unfortunately, several problems exist in present delivery systems due to the necessity of an air eliminator. A first problem with the air eliminator is the overall size required for some applications. For example, the rate of separation for high viscosity products, such as oil based petroleum products, results in the need for a large air eliminator. Similarly, high viscosity products require a longer retention time for separation that results in slower fluid delivery and a less efficient delivery system.
A second problem with air eliminators is that products such as fuel oil, diesel oil, and kerosene, often foam up as they pass through the delivery system causing air to discharge in the form of vapor. The vapor from these products is hazardous and cannot be discharged directly into the atmosphere, thus requiring a separate storage tank to accommodate vented vapors.
A third but related problem with air eliminators is the cost added to the delivery system by the inclusion of the air eliminator and in some cases a storage tank for vented vapor. For example, in delivery systems designed for heavy oils, the required tank size is so large that it is often more economical to prevent the entrance of entrained air rather than remove it during delivery. In this case, however, various additional and expensive precautions must be taken that significantly add to the transportation and storage cost for these products.
It is known in the art to use mass flowmeters to measure mass flow and other information for materials flowing through a conduit. Some types of mass flowmeters, especially Coriolis flowmeters, are capable of being operated in a manner that performs a direct measurement of density to provide volumetric information through the quotient of mass over density. See, e.g., U.S. Pat. No. 4,872,351 to Ruesch assigned to Micro Motion for a net oil computer that uses a Coriolis flowmeter to measure the density of an unknown multiphase fluid. U.S. Pat. No. 5,687,100 to Buttler et al. teaches a Coriolis effect densitometer that corrects the density readings for mass flow rate effects in a mass flowmeter operating as a vibrating tube densitometer.
Coriolis flowmeters directly measure the rate of mass flow through a conduit.
As disclosed in U.S. Pat. Nos. 4,491,025 (issued to J. E. Smith et al. on Jan. 1, 1985, hereinafter referred to as the U.S. Pat. No. 4,491,025) and U.S. Pat. No. Re. 31,450 (issued to J. E. Smith on Feb. 11, 1982, hereinafter referred to as U.S. Pat. No. Re. 31,450, these flowmeters have one or more flowtubes of straight or curved configuration. Each flowtube configuration in a Coriolis mass flowmeter includes a set of natural vibration modes, which could be of a simple bending, torsional or coupled type. Fluid flows into the flowmeter from the adjacent pipeline on the inlet side, is directed through the flowtube or tubes, and exits the flowmeter through the outlet side of the flowmeter. The natural vibration modes of the vibrating fluid filled system are defined in part by the combined mass of the flowtubes and the fluid within the flowtubes. Each flow conduit is driven to oscillate at resonance in one of these natural modes.
When there is no flow through the flowmeter, all points along the flowtube oscillate with identical phase. As fluid begins to flow, Coriolis accelerations cause each point along the flowtube to have a different phase. The phase on the inlet side of the flowtube lags the driver, while the phase on the outlet side leads the driver. Sensors can be placed on the flowtube to produce sinusoidal signals representative of the motion of the flowtube. The phase difference between two sensor signals is proportional to the mass flow rate of fluid through the flowtube. A complicating factor in this measurement is that the density of typical process fluids varies. Changes in density cause the frequencies of the natural modes to vary. Since the flowmeter""s control system maintains resonance, the oscillation frequency varies in response. Mass flow rate in this situation is proportional to the ratio of phase difference and oscillation frequency.
The Coriolis flowmeter is intended for use in environments where multiphase flow exists. Multiphase flow is defined as flow including at least two states of matter: solid, liquid or gas. The flowmeter is especially useful in multiphase systems including gas and liquid or gas and solids. These environments are especially common in the petroleum industry where a petroleum product is delivered from a source to a destination. Unfortunately, Coriolis flowmeters have not been used in petroleum delivery systems, in part, because they measure mass, as opposed to volume, and the sales of petroleum take place in volume. Furthermore, while these meters can functionally detect multiphase flow they cannot remove a gas or solid from the flow, and therefore, an air eliminator would still be required.
The present invention overcomes the problems outlined above and advances the art by providing a fluid delivery system that includes a Coriolis mass flowmeter to eliminate the need for an air eliminator and/or a strainer. In a first embodiment of the present invention, the fluid delivery system comprises a Coriolis mass flowmeter, a pump, and a recirculation valve. The pump is connected to the fluid source and the input end of the Coriolis mass flowmeter. The recirculation valve is connected to the output end of the Coriolis mass flowmeter, the fluid source, and the destination for the fluid. The recirculation valve operates under the control of the meter to prevent the measurement of a multiphase fluid flow during priming of the system. During system priming the meter electronics control the recirculation valve to direct multiphase fluid flow containing entrained air back to the fluid source until a substantially pure fluid flow is established. Once a substantially pure fluid flow is established, the meter electronics again control the recirculation valve to direct the fluid flow to the destination and begin measurement of the delivered fluid. The pump also operates under the control of the meter to start and stop the delivery of the fluid through the fluid delivery system. In some examples of the present fluid delivery system, a back-pressure valve could also be included to prevent the back-flow of fluid through the delivery system when the system is shut down. In the context of this application, system priming is defined as the establishment of a substantially pure fluid flow following the introduction of a multiphase fluid flow. System priming is required any time air is introduced into the system, which typically occurs when the system does not remain full, such as during system shut down or where the source is emptied. One skilled in the art will appreciate that this embodiment is ideal for fluids such as milk, kerosene and gasoline that have a tendency to foam during delivery or until the system is primed. In these environments, the flowmeter prevents measurement and delivery to the destination until a substantially pure flow is established.
In a second embodiment of the present invention, the delivery system comprises a Coriolis mass flowmeter, a pump, and a back-pressure valve. The pump is connected to the fluid source and the input end of the Coriolis mass flowmeter. The back-pressure valve is connected to the output end of the meter and the destination for the fluid. The pump operates under the control of the meter to stop the delivery of the fluid in response to the detection of a multiphase fluid flow through the meter. The back-pressure valve also operates under the control of the meter to prevent back-flow of fluid through the delivery system when the system is shut down. This embodiment is ideal for liquefied compressed gases that change from a liquid to a gas as the source is emptied and the pressure approaches atmospheric pressure. In response to detecting the presence of a multiphase flow, the Coriolis mass flowmeter shuts down the pump and closes the back-pressure valve to prevent the measurement of the multiphase flow. When the source is again filled, bringing the pressure back to the pressure required for the liquid state of the liquefied compressed gas, any material in the gas state returns to the liquid state. Thus, the pump can again be started and the back-pressure valve opened for further delivery of the liquefied compressed gas.
The Coriolis mass flowmeter is capable of use as a vibrating densitometer in multiphase flow environments including combinations of gas and liquids, gas and solids, or solids and liquids. The flowmeter includes at least one flowtube and a driver for vibrating the flowtube at a fundamental frequency corresponding to a density of material flowing through the flowtube. The meter electronics monitor the vibrating flowtube(s) for changes in the density value of the fluid product to determine the existence of a multiphase flow through the meter. During meter operation, the density value is compared against a threshold value where multiphase flow including gas and liquid is indicated by the measured density value exceeding a threshold value. A second comparison could be made against a second threshold value to indicate the existence of multiphase flow including gas and solids, liquid and solids, or liquid, gas and solids, which could exhibit similar damping effects to those of gas and liquid systems. The meter electronics respond to the existence of multiphase flow in the flowtube(s) and provide output signals to the pump, the recirculation valve, and back-pressure valve to either stop delivery of the fluid or redirect the fluid delivery back to the source to prevent measurement and delivery of a multiphase flow.
A first advantage of the present delivery system is that an air eliminator is not required. The present delivery system is configured to either stop the flow of fluid product through the system or redirect the flow back to the fluid source in response to the detection of a multiphase product flow. Thus, in the first embodiment above, the fluid product is redirected back to the source to establish a substantially pure fluid flow before delivery to the destination and measurement. In the second embodiment above, the fluid delivery system stops delivery of the fluid altogether in response to detection of a multiphase fluid flow. A second advantage of the present delivery system is that the Coriolis mass flowmeter is intended for use in any environment where multiphase flow exists. Thus, the present delivery system does not require a strainer to prevent the intrusion of grit and other foreign matter that can damage downstream components. Upon detection of foreign matter, the meter controls the recirculation valve and back-pressure valve where included, to either stop delivery of the fluid product or redirect delivery back to the fluid source.
Therefore, an aspect of the present invention comprises:
a fluid delivery system for measuring a substantially pure fluid product flow and preventing measurement of a multiphase fluid flow during delivery of a fluid product from a fluid source to a destination;
a pump connected between the fluid source and the destination for delivering the fluid product from the fluid source to the destination;
a Coriolis mass flowmeter connected between the pump and the destination and configured to detect a beginning of the multiphase fluid flow as the fluid product is delivered from the fluid source to the destination;
a back-pressure valve connected between the Coriolis mass flowmeter and the destination and configured to open or close under the control of the Coriolis mass flow meter;
means within the Coriolis mass flowmeter for controlling the pump in response to detecting the beginning of the multiphase fluid flow to cause the pump to stop delivery of the fluid product from the fluid source to the destination; and
means within the Coriolis mass flowmeter for controlling the back-pressure valve in response to detecting the beginning of the multiphase fluid flow to cause the back-pressure valve to close, wherein the Coriolis mass flowmeter uses the pump controlling means and the back-pressure valve controlling means to prevent the measurement of the multiphase fluid flow by stopping delivery of the fluid product in response to detecting the beginning of the multiphase fluid flow.
Another aspect is:
a recirculation valve that is connected to the Coriolis mass flowmeter, the fluid source, and the destination, and is configured to direct the fluid product in a first direction that terminates at the fluid source and a second direction that terminates at the destination.
Another aspect is:
a means within the Coriolis mass flowmeter for controlling the recirculation valve in response to detecting the beginning of the multiphase fluid flow to cause the recirculation valve to direct the fluid product in the first direction, wherein the Coriolis mass flowmeter uses the pump controlling means and the recirculation valve controlling means to prevent the measurement of the multiphase fluid flow by causing the recirculation valve to direct the fluid product in the first direction back to the fluid source.
Another aspect is:
a fluid delivery system wherein the back-pressure valve is configured to provide back pressure in the fluid delivery system.
Another aspect is:
meter electronics electrically connected to the recirculation valve and configured to provide a first output signal to the recirculation valve in response to detecting the beginning of the multiphase fluid flow that causes the recirculation valve to direct the fluid product in the first direction back to the fluid source.
Another aspect is:
meter electronics that are electrically connected to the pump and configured to provide a second output signal to the pump in response to detecting the beginning of the multiphase fluid flow that causes the pump to stop delivery of the fluid product from the fluid source to the destination.
Another aspect is:
meter electronics that are electrically connected to the back-pressure valve and configured to provide a third output signal to the back pressure valve in response to detecting the beginning of the multiphase fluid flow that causes the back pressure valve to provide the back-pressure in the fluid delivery system.
Another aspect is:
meter electronics that are configured to measure a density value of the fluid product and if the density value is greater than an upper threshold density value, provide at least one of the first, the second, and the third output signals.
Another aspect is:
meter electronics that are configured to measure the density value of the fluid and if the density value is lower than a lower threshold density value provide at least one of the first, the second, and the third output signals.
Another aspect is:
meter electronics that are configured to measure the density value of the fluid product and if the density value is equal to the upper threshold density value provide the at least one of the first, the second, and the third output signals.
Another aspect is:
meter electronics that are configured to measure the density value of the fluid product and if the density value is equal to the lower threshold density value provide the at least one of the first, the second, and the third output signals.
Another aspect is:
A method for measuring a fluid product flow during delivery of a fluid product from a fluid source to a destination comprising the steps of:
delivering a fluid product from the fluid source to the destination;
detecting a beginning of a multiphase fluid flow as the fluid product is delivered from the fluid source to the destination;
providing a first output signal to a pump to stop delivery of the fluid product in response to detecting the beginning of the multiphase fluid flow; and
providing a second output signal to a back-pressure valve to provide back-pressure in response to detecting the beginning of the multiphase fluid flow.
Another aspect is:
measuring a density value of the fluid product as the fluid product is delivered from the fluid source to the destination; and
comparing the measured density value to an upper threshold density value, wherein the multiphase fluid flow is indicated by the measured density value being greater than the upper threshold density value.
Another aspect is a fluid delivery system for measuring a substantially pure fluid product flow and preventing measurement of a multiphase fluid flow during delivery of a fluid product from a fluid source to a destination, the fluid delivery system comprising:
a pump connected between the fluid source and the destination for delivering the fluid product from the fluid source to the destination;
a Coriolis mass flowmeter connected between the pump and the destination and configured to detect a beginning of the multiphase fluid flow as the fluid product is delivered from the fluid source to the destination;
a recirculation valve that is connected to the Coriolis mass flowmeter, to the fluid source, and to the destination, and is configured to direct the fluid product in a first direction that terminates at the fluid source and a second direction that terminates at the destination; and
means within the Coriolis mass flowmeter for controlling the pump in response to detecting the beginning of the multiphase fluid flow to cause the pump to stop delivery of the fluid product from the source to the destination.
Preferably a back-pressure valve is connected between the Coriolis mass flowmeter and the destination and configured to open or close under the control of the Coriolis mass flow meter; and
means within the Coriolis mass flowmeter for closing the back-pressure valve in response to detecting the beginning of the multiphase fluid flow; to cause the back-pressure valve to close;
said Coriolis mass flowmeter prevents the measurement of a multiphase fluid flow by operating the pump controlling means and the back-pressure valve controlling means to stop the delivery of the fluid product in response to the detecting of the beginning of the multiphase fluid flow.
Another aspect is:
measuring the density value of the fluid product as the fluid product is delivered from the fluid source to the destination; and
comparing the measured density value to an upper threshold density value, wherein the multiphase fluid flow is indicated by the measured density value being equal to the upper threshold density value.
Another aspect is:
measuring the density value of the fluid product as the fluid product is delivered from the fluid source to the destination; and
comparing the measured density value to a lower threshold density value, wherein the multiphase fluid flow is indicated by the measured density value being lower than the lower threshold density value.
Another aspect is:
measuring the density value of the fluid product as the fluid product is delivered from the fluid source to the destination; and
comparing the measured density value to the lower threshold density value, wherein the multiphase fluid flow is indicated by the measured density value being equal to the lower threshold density value.